The present invention relates to an evaporated fuel treatment device of an engine.
Known in the art is an internal combustion engine, provided with a canister for temporarily storing evaporated fuel, a purge control valve for controlling the amount of purge gas to be purged from the canister to the inside of an intake passage downstream of a throttle valve, and an air-fuel sensor arranged in the engine exhaust passage, which controls an opening degree of the purge control valve so that the ratio between the amount of purge gas and the amount of intake air, that is, the purge rate (=amount of purge gas/amount of intake air), becomes a target purge rate, finds an amount of fuel vapor purged from an amount of deviation of the air-fuel ratio from a stoichiometric air-fuel ratio based on an output signal of the air-fuel ratio sensor, and corrects downward the amount of fuel injection by exactly an amount corresponding to the amount of fuel vapor so that the air-fuel ratio becomes the stoichiometric air-fuel ratio (see Japanese Unexamined Patent Publication (Kokai) No. 5-52139). In that internal combustion engine, when the purge action was started, the target purge rate was made to gradually increase. The target purge rate was held at a constant value after the elapse of a predetermined time from the start of the purge action.
In this way, this internal combustion engine corrects downward the amount of fuel injection by exactly an amount corresponding to the amount of fuel vapor so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. That is, the amount of fuel injection is corrected downward so that the ratio of the intake air and the sum of the amount of fuel vapor and amount of fuel injection becomes the stoichiometric air-fuel ratio. The amount of fuel adsorbed in the activated carbon in the canister, however, changes according with the operating state of the engine. Therefore, even if the purge rate is held constant, the amount of fuel vapor to be purged changes in accordance with the operating state of the engine. If the amount of fuel vapor to be purged changes, the ratio of reduction of the amount of fuel injection changes along with this and as a result the ratio of the amount of fuel vapor to the amount of fuel injection changes.
If the ratio of the amount of fuel vapor with respect to the amount of fuel injection changes in this way, however, there is the problem that the downward correction of the amount of fuel injection will not be fast enough right after the change occurs and therefore the air-fuel ratio will end up deviating from the stoichiometric air-fuel ratio temporarily.
Further, depending on the internal combustion engine, sometimes the amount of fuel vapor as compared with the amount of fuel injection has a large effect on the combustion. In such a case, it becomes necessary to maintain the ratio of the amount of fuel vapor to the amount of fuel injection at a predetermined ratio. Therefore, in such an internal combustion engine, the problem arises that the combustion will end up deteriorating even if the purge rate is maintained constant.
For example, when designed to form an air-fuel mixture in a limited region in the combustion chamber, as explained later, there is an optimal value to the ratio of the amount of fuel vapor to the amount of fuel injection. If the ratio of the amount of fuel vapor to the amount of fuel injection deviates from this optimal value, problems such as misfire will arise. Therefore, if the ratio of the amount of fuel vapor with respect to the amount of fuel injection ends up changing, the ratio of the amount of fuel vapor to the amount of fuel injection will deviate from the optimal value and therefore problems such as misfires will occur.
In this way, in the above known internal combustion engine, problems like the above arose when looking at the ratio of the amount of fuel vapor to the amount of fuel injection, but the following problems also arose when changing the perspective a bit and looking at the ratio of the amount of purge gas to the amount of fuel injection.
That is, the purge rate is held constant as in the above mentioned known internal combustion engine so as to prevent the air-fuel ratio from fluctuating when the amount of intake air changes. That is, if the purge rate changes when the amount of intake air changes, the ratio of the amount of purge gas in the intake air changes and as a result the air-fuel ratio changes. Therefore, the purge rate is made to be maintained constant so that the ratio of the amount of purge gas in the intake air does not change even if the amount of intake air changes. In this way, not limited to the above known internal combustion engine, in internal combustion engines in general designed for purge control, the purge operation is controlled so that the purge rate becomes constant, that is, so that the amount of purge gas increases in proportion to the amount of intake air.
In an internal combustion engine designed for purge control in the past, however, the amount of fuel injection was increased along with the increase of the amount of intake air and therefore the output of the engine was increased. That is, in this internal combustion engine, the output of the engine was controlled by adjusting the amount of intake air. In such an internal combustion engine, the amount of fuel injection is increased along with an increase of the amount of intake air and therefore if increasing the amount of purge gas along with an increase of the amount of intake air, it becomes possible to maintain the air-fuel ratio constant without accompanying fluctuation of the engine output.
Depending on the internal combustion engine, however, if the purge rate is maintained constant, the output will fluctuate and the exhaust emission will deteriorate. A typical example of such an internal combustion engine is a stratified combustion type internal combustion engine designed to form an air-fuel mixture inside a limited region of a combustion chamber. In such an internal combustion engine, the air-fuel mixture is burned under an excess of air, so even if the amount of intake air is increased, the output of the engine will not increase. Increasing the output of the engine requires an increase in the amount of fuel injection. That is, in this type of internal combustion engine, the output of the engine is controlled by adjusting the amount of fuel injection. In such an internal combustion engine, generally speaking, the ratio of the amount of intake air to the amount of fuel injection becomes larger or smaller in accordance with the operating state.
In such an internal combustion engine, however, if the purge rate is maintained constant in the same way as a conventional internal combustion engine, that is, if the amount of purge gas is increased along with an increase of the amount of intake air, the ratio of the amount of purge gas to the amount of fuel injection will become larger or smaller in accordance with the operating state of the engine. If the ratio of the amount of purge gas to the amount of fuel injection becomes larger or smaller in this way, the output of the engine will increase or decrease along with this. Further, if the ratio of the amount of purge gas to the amount of fuel injection increases, the exhaust emission will deteriorate. Therefore, the problem arises that if the amount of purge gas is changed in proportion to the amount of air intake as in the conventional internal combustion engines, the output of the engine will fluctuate and the exhaust emission will deteriorate.
An object of the present invention is to provide an evaporated fuel treatment device of an internal combustion engine capable of ensuring good engine operation even if feeding purge gas.
According to the present invention, there is provided an evaporated fuel treatment device of an internal combustion engine provided with a purge passage for purging fuel vapor generated in a fuel tank into an intake passage; a purge control valve for controlling the amount of purge gas to be purged from the purge passage to the inside of the intake passage; an injection calculating means for calculating an amount of fuel injection; a setting means for setting a target value of a fuel vapor rate showing a ratio of the amount of fuel vapor in the purge gas to the amount of fuel injection; and a control means for controlling at least one of the amount of purge gas and the amount of fuel injection so that the fuel vapor rate become the target value.
Further, according to the present invention, there is provided an evaporated fuel treatment device of an internal combustion engine provided with a purge passage for purging fuel vapor generated in a fuel tank into an intake passage; a purge control valve for controlling the amount of purge gas to be purged from the purge passage to the inside of the intake passage; an injection calculating means for calculating an amount of fuel injection; a setting means for setting a target value of a purge gas rate showing a ratio of the amount of purge gas to the amount of fuel injection; and a control means for controlling at least one of the amount of purge gas and the amount of fuel injection so that the purge gas rate become the target value.